On Tuesday, six people will be voluntarily locked into a cloister of cramped, hermetically sealed tubes woven inside a Moscow research facility the size of a high school gymnasium. They will eat dehydrated food, breathe recycled air and be denied conversation with practically everyone else but one another.

And they must stay inside for 105 days.

In a small step in the direction of Mars, the international crew is embarking on a simulated flight to the planet to test the limits of human tolerance for the isolation and monotony of interplanetary travel.

“It is really like a real space flight without the weightlessness and the danger to our lives,” said Sergei N. Ryazansky, a cosmonaut-in-training who will lead the mission. “On the inside, we will have a lack of incoming information, so it’s the science of sensory deprivation.”

Called Mars-500, the Russian-led project based at the Institute for Biomedical Problems here will culminate in a 520-day simulation beginning early next year of a complete manned mission to the planet — a time frame that incorporates launching to Mars touchdown and back — that scientists hope will edge humanity a little closer to that next giant leap.

It sounds a little crazy, but maintaining crew sanity for a year-and-a-half trip is at least as important and perhaps even as daunting as the engineering challenges of making such a trip technically possible.